Many modern power station installations, which are equipped with gas turbines in order to generate electrical power, also have one or more waste heat boilers in order to use the hot exhaust gas from the gas turbines (which still has a high energy potential after being ejected from the gas turbine) for further conversion to usable power. In this case, for example, the steam generated by the waste heat boiler is used for operation of at least one steam turbine, so the efficiency of a gas and steam power station such as this is higher than that of a pure gas turbine power station.
In addition to the steam turbine, modern gas and steam power stations require auxiliary steam for widely differing further consumers (for example bypass flow degasifiers, building heating, etc.).
This auxiliary steam is required in particular when the installation is not in use and when starting up and/shutting down the turbine sets, as well as during normal operation of the power station installation, for example at the rated load.
When the installation is not in use, the gas turbine does not emit any hot exhaust gas, so that no operating steam, and no auxiliary steam either, can be provided by means of the waste heat boiler in this operating situation for the steam turbine or for further steam consumers, as mentioned by way of example above.
In order to supply steam consumers such as these with auxiliary steam, an independent, heated auxiliary steam generator, which is completely isolated from the waste heat steam generator, is generally used in known power stations.
Auxiliary steam generators such as these generate saturated steam, that is to say superheated steam, when the installation is not in use and during starting up/shutting down, and this is supplied to the steam consumers mentioned above.
During normal operation of the installation, the auxiliary steam that is required is generated, for example, in a low-pressure section of the waste heat steam generator while, during normal operation, the auxiliary steam generator, which is designed such that it is separate from the waste heat steam generator, is not necessarily required, since the auxiliary steam can be generated in the waste heat steam generator itself, from the hot exhaust gas that is introduced into it.
Dispensing with the auxiliary steam generator in a known power station installation is often possible only in exceptional situations (for example in the case of pure basic load power stations which operate virtually around the clock and in which hot exhaust gas is therefore available all the time for auxiliary steam generation), and leads to considerable restrictions on the flexibility of the installation since, for example, a complete installation shut down or operation at a very low load leads to loss of the auxiliary steam generation.
Further requirements for power station installations include heating up, keeping hot and maintaining the pressure in the waste heat boiler and the fresh steam lines, as well as heating up and keeping hot the steam turbine at a temperature and a pressure level which are as high as possible; the stated requirements should also be satisfied when the installation is not in use and while the turbines are being started up or shut down.
By way of example, the starting-up time for a known power station installation is dependent on the pressure and the temperature of the auxiliary steam.